Further studies on the chemistry and biology of tritiated acetamidino parathyroid hormone are proposed in order to understand the chemical nature of the hormone, the relationship of this structure to its function, the primary interactions of the hormone with kidney receptors, the metabolism of the hormone by the kidney, and the physiological significance of these processes. Binding of the hormone to plasma membranes from kidney will be studied and attempts made to increase the sensitivity of this interaction. New methods of membrane preparation and assay procedure will be studied, as well as the metabolism of hormone by the membranes. Successful demonstration of physiologically significant binding will be followed by investigation of the chemical nature of the interaction. The correlation between binding and membrane structure will be studied. Relationship of adenylate cyclase will be investigated. Isolated kidney tubules will also be used for such work and attempts made to identify the cell types which contain parathyroid hormone receptors. Hormone metabolism will be studied in intact rat kidney, perfused rat kidneys, isolated rat and beef tubules and isolated cell fractions. Identification of the primary products of hormone metabolism in the sequence and mechanism of their production, and their biological function, if any, will be studied. Analysis of tissue radioactivity, as well as venous and ureter output by the intact kidney will be studied as a function of time and metabolic state of the animal. Attempts will be made to identify, characterize, and isolate any specific enzyme implicated in the process of parathyroid hormone metabolism in the kidney.